Method of increasing wax absorption rates of porous paper products

ABSTRACT

The rate at which a porous paper product absorbs paraffin waxes having a melting point of at least 136* F. (AMP) at an impregnation temperature less than 17* F. greater than the melting point of said wax is substantially increased by the addition of a small amount of an ester or mixture of esters of a fatty acid and a polyhydric alcohol to the wax before application.

United States Patent WA X IMPREGNATION TIME OF POROUS PAPER PRODUCTS, SECONDS 2,204,612 6/ 1940 Musher 106/245 X 2,483,259 9/1949 Budner et a1. 106/245 3,061,456 10/1962 Davis et a1. 117/158 X 3,177,091 4/1965 Case et a1. 117/158X 3,194,677 7/1965 Schwarz et a1. 1 17/158 X 3,231,462 1/1966 Oswald et a1. 117/158 X 3,271,177 9/1966 Rumberger..... 117/158 X 3,305,392 2/1967 Britt 117/158 X 3,312,564 4/1967 Barbour 117/158 X 3,332,798 7/1967 Kautsky 1 17/158 X Primary Examiner-William D. Martin Assistant Examiner-M. R. Lusi nan AuorneysGeorge L. Church, Donald R. Johnson and Wilmer E. McCorquodale, Jr.

ABSTRACT: The rate at which a porous paper product absorbs paraffin waxes having a melting point of at least 136 F. (AMP) at an impregnation temperature less than 17 F. greater than the melting point of said wax is substantially increased by the addition of a small amount of an ester or mixture of esters of a fatty acid and a polyhydric alcohol to the wax before application.

FOR HIGH MELTING POINT WAXES KEY CONCENTRATION OF ADDITIVE l WITHOUT ADDITIVE 2 0.01 WT 3 0.05 WT 4 0.50 WT 0- TMP TBP H-APPLICATION TEMPERATURE-D1 TEMPERATURE, "F

Pmmmm 41m 3532.426

FOR HIGH MELTING POINT WAXES KEY CONCENTRATTON OF ADDITIVE l WITHOUT ADDITNE O T P TX TBP HAPPL|CATION TEMPERATURE-M TEMPERATURE, F

INVENTORS EDWARD M. KOHN ALEXANDER D. RECCHUITE BY LQQMJ ATTORNEY METHOD OF INCREASING WAX ABSORPTION RATES OF POROUS PAPER PRODUCTS BACKGROUND OF THE INVENTION The present invention provides a method for increasing the rate at which paraffin waxes will be absorbed by a porous paper product. This method produces an impregnated paper product in a substantially reduced amount of time thereby increasing the rate of product output of existing equipment when operating within a certain temperature range. In addition, the increased product output can be achieved at a lower temperature thereby reducing the operating cost of heating the wax.

Porous paper products, such as paperboard, corrugated paperboard, paper cup stock, are impregnated with paraffin waxes and the resulting wax-impregnated products are used for many purposes. In the manufacture of these wax-impregnated products it is necessary, because of competitive economic alternatives, that the system makes the product at the highest rate possible consistent with satisfactory product quality and at as low cost as is possible. This invention helps meet these requirements.

SUMMARY OF THE INVENTION The present invention provides a process by which, at certain temperatures, the rate of absorption of high-melting point paraffin waxes by a porous paper product is substantially increased. In addition this increased absorption rate is accomplished with a decrease in utility costs.

According to the invention, the increased parafiin wax impregnation rate is obtained by the addition of a small quantity of ester or mixture of esters of a C -C fatty acid with a polyhydric alcohol having two to five carbon atoms and two to three hydroxyl groups to the wax and thereafter applying the mixture to the porous paper product. The increase in rate of paraffin wax impregnation is obtained when the application temperature is less than 17 F. greater than the melting point of the wax. Thus, when the temperature of application of the mixture is 17 F. greater than the melting point of the parafiin wax, the ester in the wax does not increase the rate of impregnation.

DESCRIPTION OF THE DRAWING The graph in the drawing plots wax impregnation time of porous paper products versus application temperature. This graph shows the effectiveness of the ester additive on highmelting point wax impregnation rates of porous paper products over a narrow temperature range. A portion of line 1 between the melting point of the wax, Tup, and some higher temperature, T shows that as the application temperature increases the impregnation time decreases. The balance of line 1, between T and the boiling point of the wax, Tap, shows that impregnation time is substantially independent of the application temperature in this higher temperature range. Dashed lines 2, 3 and 4 show that the ester additive in the wax reduces impregnation time between temperatures T and T Dashed lines 2, 3 and 4 also show that, at any given temperature between T and T impregnation time decreases as the concentration of the additive increases.

DESCRIPTION ln practicing the invention, parafi'm wax, which is applied to the porous paper product has incorporated into it a small amount of an ester or mixture of esters from a fatty acid, and a polyhydric alcohol. The ester, used in this invention, can be a reaction product between a fatty acid having eight to 30 carbon atoms and a polyhydric alcohol containing two to five carbon atoms and two to three hydroxyl groups. Fatty acids refer to aliphatic monocarboxylic acids, both saturated and unsaturated, such as caprylic, n-nonadecylic, melissic, obtusilic, oleic, hiragonic, moroctic, stearolic, etc., but such acids as palmitic, stearic, oleic and linoleic are commercially available and therefore their esters are preferred in practicing the invention. Ethylene glycol, propylene glycol and glycerol are the preferred polyhydric alcohols; however, others such as 1.4- butanediol; l,5-pentanediol; 1,2,4-butanetriol; pentanetriols; etc. can be used to prepare the ester additive.

A more specific group of the esters previously discussed are the glycerides, the manufacture of which is discussed in Kirk and Othmer, ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, Copyright 1965, 2nd Edition, Volume 8. A mixture of mono-, diand triglycerides is formed from the glycerol esterification of fatty acids. The maximum concentration of the monoglyceride in the mixture after removal of the reactants and by-products but without further processing is about 60 percent by weight. A monoglyceride fraction with a monoester concentration of about percent by weight can be obtained by molecular distillation. While a glyceride with a monoester content of about 90 percent by weight is usedto illustrate the invention, lower monoester contents will work almost as well. The level of purity depends, in part, on whether the wax-coated article is intended to be used in contact with food.

When this invention is used to prepare a wax-impregnated paper product that will be in contact with food it is distinctly preferably that the fatty acid group of the glyceride, for example, be derived from an edible fat, since it willbe hannless in case any of the monoglyceride seeps into the food product. An example of such a monoglyceride is glycerol monooleate.

The glycerol monooleate or other ester as above specified is incorporated in the wax by mixing asmall' amount of it with molten wax. While the proportion of ester incorporated in the wax can range from about 0.005 percent to about 1.0 percent by weight, generally the range will be from about 0.01 percent to 0.50 percent by weight.

Many kinds of porous paper products can be impregnated with wax. Among these are paperboard, corrugated paperboard, kraft, sulfite and paper cup stock. The latter is used in our examples to demonstrate the principle of our invention; it will work equally well on other kinds of porous paper products.

Parafi'ln waxes are available witha wide range of physical properties, for example, melting points may be as low as l00 F. or as high as F. However, for reasons discussed hereinafter the present invention utilizes only those paraffin waxes with melting points equal to or greater than 136 F. (AMP). The preferred melting point range of the wax is l36 to 160 F. (AMP).

The ester additive efiect on wax impregnation rate by porous paper products depends on the type of the wax, the

melting point of the wax, the temperature of application, and the concentration of the additive. Surprisingly-the ester does not decrease wax impregnation time for all waxes. The ester does not affect impregnation time of microcrystalline waxes but does for certain paraffin waxes. impregnation rates of paraffin waxes with melting points of 136 F. (AMP) or higher have been found to be influenced by the additive.

The temperature at which the molten combination of paraffin wax and ester is applied to the porous paper product can affect the impregnation rate, as indicated by the solid line in the drawing. When the temperature difi'erence between the temperature of application and the melting point of the paraffin wax is small, the addition of the ester to the wax reduces the time required for the combination of wax and ester to impregnate the paper product. However, as the temperature of application increases and the difference between the temperature of application and the melting point of the wax becomes larger and larger the additive in the wax has less and less effect on the time required to impregnate the porous paper product. As the temperature increases the difference becomes sufficiently great so that the additive in the wax has no effect on the time required to impregnate the paper product.

One explanation of this phenomenon is as follows. When the difference between the temperature of application and melting point of wax is small the solution forces of the wax to dissolve the ester are low and the ester thereby has a strong wetting efi'ect on the paper when the mixture is applied thereto. However when the temperature difference is large, the solution forces of the wax to dissolve the ester are much greater and the ester then has no appreciable wetting effect on the paper. For paraffin waxes with melting points equal to or greater than 136 F. (AMP) the improvement in wax impregnation rate is secured when the temperature difference between the application temperature and the waxs melting point is less than 17 F.

The concentration of the ester additive in the wax also affects the impregnation time as indicated by the dashed lines in a trough with a circular orifice on the upper surface. The cup stock is placed over the orifice and held thereby a glass plate and clamp. The glass plate allows the operator to observe the test area of the cup stock.

The wax was brought into contact with the cup stock by tilting the trough down. This action activates a timer. When the operator saw that the cup stock was impregnated completely he tilted the trough up automatically stopping the timer.

Table II below lists the impregnation data obtained with the penetrometer for the waxes given in table 1 when said waxes were mixed with various concentrations of additive.

The application temperatures ofruns 1. 5. and 8 are in that TABLE II Difference between melting Time to impregnate, seconds wuighi Percent weight of additive:

weight of additive weight of wax X100 1 Additive is defined in examples.

the drawing. With only 0.01 percent of additive in the wax gT temperature range where increases in temperature decrease the ester additive in the wax ranges from 0.5 to 1.0 weight per- 40 cent.

EXAMPLES Table I below lists some of the physical properties of highmelting point paraffin waxes used to illustrate the invention. These waxes were used in the runs listed in table II.

TABLE I Paraffin Wax A B C Physical properties Melting point, "F. (AMP') 156 I43 I35 Viscosity, SUS at 210 F. 44.8 39.8 38.8

AMP is the American Melting Point which is 3 F. higher than the ASTM melting point.

The paraffin wax was placed in a beaker and heated till its temperature was about 10 F. above its melting point. The ester, in the desired amount, added to the melted wax. One cubic centimeter of a suitable dye was added to every 1,000 g. of wax and ester. The dye-aided in visual observations.

The ester used was glycerol monooleate. This monooleate had a minimum monoester content of 90.0 percent; saponification value of 155-165, iodine value 65-70, a maximum glycerol content of 1.0 percent, a maximum free fatty acid impregnation time or, in other words, in the range from T to T as shown in the drawing. Within this temperature range the from 0.01 weight percent to 0.05 weight percent and then to 0.5 weight percent there was a consistent downward trend in the time required to impregnate the cup stock. Thus, with 0.5 weight percent of ester in wax A the average impregnation time is 16.8 seconds. This is a reduction in the average impregnation time of about 20 percent.

Each impregnation time shown in table 11 is the arithmetic average of nine trials.

Run 2, with no additive, at an application temperature of 180 F. shows an average impregnation time of 17.3 seconds. As the application temperature is increased to 190 or 200 F as in runs 3 and 4, there is no statistical significant change in impregnation time compared to run 2. This indicates that above a certain application temperature increases in the application temperature does not decrease impregnation time.

The application temperature of run 1, without additive, while 14 F. greater than the melting point of the wax, is still within the temperature range where changes in application temperature change impregnation rates. Yet at an application temperature 17 F. greater than the melting point of the wax, as in run 6, without additive, further increases in application temperature did not cause changes in impregnation times. Thus, at a temperature less than 17 F. greater than the melting point of the wax a change takes place. This temperature is T in the graph in the drawing. The change referred to is that at some temperature smaller than T changes in application content f 5 percent (as l i a specifi gravity f temperature cause changes in impregnation rates, while at a 0.95-0.96 at 40 C. and a melting point of 29 to 35 C.

The wax-estendye mixture was placed in a penetrometer. This instrument measures the time required for molten wax at a fixed temperature to impregnate a sample of cup stock or temperature greater than T changes in application temperature do not cause changes in impregnation rates.

Thus the addition of the ester to the paraffin wax increase the impregnation rate or, in other words, decreases the time porous paper products. About 700 cc. of wax are contained in required for impregnation when the application tempflam'e is less than the temperature, T as defined herein. This is shown by run 1. The addition of the ester to the paraffin wax has no effect on the impregnation rate when the application temperature is greater than the temperature, T as defined herein. This is shown by runs 2 to 10.

In these examples the outside of the cup stock was treated. However, the invention is equally applicable to treatment of the inside of the cup stock.

Substantially equivalent results, as in the above specific examples, are obtained when (1) other paraffin waxes melting above 136 F. are used, (2) other esters as herein specified are used including mono-, diand triesters of other C -C fatty acids with C -C polyhydric alcohols having two to three hydroxyl groups or mixtures of such esters and/or (3) other porous paper products as herein specified are used.

The invention claimed is:

1. In the impregnation of porous paper with a molten paraffin wax having a melting point of at least 136 F. (AMP), the improvement which comprises utilizing as the impregnating composition said parafiin wax having incorporated therein from 0.01 percent to 1.0 percent by weight of an additive which is an ester or mixture of esters of a C -C fatty acid with a polyhydric alcohol having two to five carbon atoms and two to three hydroxyl groups, wherein said ester is a monoester or at least 60 percent by weight of said mixture of esters are monoesters, and impregnating the paper with said composition at a temperature less than 17 F. greater than the :meltingpoint ois lid yvax.

' of esters is present in the wax in the amount of 0.01 percent to 0.5 percent by weight.

6. Method according to claim 2 wherein the alcohol has two to three carbon atoms.

7. Method according to claim 6 wherein the paratfin wax contains a mixture of esters having about percent by weight of a monoester.

8. Method according to claim 7 wherein the mixture of esters is present in the wax in the amount of 0.01 percent to 0.5 percent by weight. 

2. Method according to claim 1 wherein the wax melts between 136* and 160* F. (AMP).
 3. Method according to claim 1 wherein the alcohol has two to three carbon atoms.
 4. Method according to claim 1 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.
 5. Method according to claim 1 wherein the ester or mixture of esters is present in the wax in the amount of 0.01 percent to 0.5 percent by weight.
 6. Method according to claim 2 wherein the alcohol has two to three carbon atoms.
 7. Method according to claim 6 wherein the paraffin wax contains a mixture of esters having about 90 percent by weight of a monoester.
 8. Method according to claim 7 wherein the mixture of esters is present in the wax in the amount of 0.01 percent to 0.5 percent by weight. 